WATER150mRESIST: A Seiko 7548-7000 from June 1982

In flagrant violation of my self-imposed rule not to buy watches with lug widths larger than 20mm, I find myself in possession of a Seiko 7548-7000 dating from June 1982 (22mm in case you were wondering). My excuse is that the bid I submitted was not entirely serious but ended up winning the auction, probably because other potentially interested parties were put off by the watch having been described as unresponsive to the fitment of a fresh battery. I confess too to a certain fondness for the model, largely because my first semi-serious attempt at a watch refurb was the fettling of a pepsi variant of the same (see here). It is also a watch to be respected because its design was born from the tail end of a golden period of creativity for Seiko and, as a result, it is a watch whose quality shines through, unencumbered by the air of penny pinching evident in the second generation 6309 automatic diver’s watch introduced three or four years later and with whom it shared its case design.

The auction photos suggested that this particular watch was in tip top nick, non-functioning movement notwithstanding, and with it in hand, that impression is not undermined.

For sure, it is a little dirty but it looks to have been very well cared for over its 33 year life time, with the dial and hands in particular looking super, the bezel original and only sporting a few minor scratches and the crown and case tube still in possession of the full quota of thread. With a movement as potentially accurate as this robust old quartz, it is perhaps not surprising that previous owners might not have had cause to undo the crown very often.

It doesn’t look either that this watch had seen much watchmaker action: the case back shows two dimples on its timeline indicating battery changes in 1985 and 1991

although, any since 1994 would not have appeared on the case back, I suppose. Still, the movement looks clean with only some tarnishing to the model number plate on the green circuit block betraying the watch’s age.

The battery is missing from this shot but when I received it, one was fitted and the watch not running, as advertised; a substitute yielded nothing in the way of meaningful action either. Its non-functioning state was enough to prompt me to pick up a very cheap but working 7546 quartz watch from eBay to farm for parts as required (I was thinking at the time that the coil was probably shot).

Slipping the movement out of the case and the dial looks every bit as good as hinted at from the exterior view, barring a slight mark to the left of the 5 marker.

Dial off and we see a calendar-side layout all but identical to the 6309 on which this movement is based

with pretty much everything looking essentially mint. The resistance offered up by the hands when I removed them suggested that this is the first time anyone has gained access to the movement innards since 1982. I’ll skip the breakdown of this side of the movement as we’ve been here before with the 6309 (see here, for example) and concentrate instead on the relative unfamiliarity of the train and circuit side.

The layout is pretty conventional with the train wheels and bridge sat in the centre, the coil at the bottom and the quartz oscillator and circuit hidden on the reverse side to the left. The gold coloured screw to the right of the movement nameplate is a trimmer condenser, used to regulate the timing of the movement.

The green circuit block is secured by four screws, two of which also secure the battery-holding spring. With it removed and turned over we can see the quartz oscillator and reset pin, the latter coming into play when the crown is pulled out to the time-setting position.

The removal of the circuit block allows access to the coil and train wheel bridge.

A slight hiccough follows because, having removed the crown with it in the time-setting position, the second setting lever (effectively the equivalent of a hacking lever) is sitting snugly against the fourth wheel, making extraction of any of the train wheels ill-advised.

Refitting the crown and stem and resetting to the normal position frees up the fourth wheel

permitting the removal of the train wheels and providing access to the centre wheel bridge.

The tarnishing of the model number plate on the circuit block was something I wanted to sort during the cleaning process. Obviously, attempting to clean it in situ is inadvisable but it is easy enough to remove by pushing the securing tabs from the rear.

Following cleaning of all of the non-electrical movement parts in the watch cleaning machine, reassembly proceeds as follows: First up, fit and lubricate, as required, the clutch and stem followed by the setting lever, yoke and setting lever spring.

Turn the movement over and fit the centre wheel and positive battery terminal connector

followed by the centre wheel bridge, rotor stator and reset lever.

The train wheels, step rotor, second setting lever and reset lever come next, with the crown set to its normal position to aid fitment of the second setting lever.

Setting the crown to its second position frees the lower part of the reset lever to move downwards against the sprung load exerted by its upper part, with the end of the stem no long sitting against the pin to the rear of the reset lever. This downwards movement simultaneously allows the second setting lever to rotate clockwise and make contact with the teeth of the fourth wheel and the end of the reset lever to move downwards and make contact with the reset pin on the rear of the circuit block.

The contact of the reset lever with the reset pin stops the output signal from the circuit block but maintains current to the quartz oscillator so that it is ready to start again when the crown is pushed back to the normal position.

The remaining steps in the reassembly of the movement are straightforward but in taking them, we need to test the function of the original coil and circuit. So, first refit the original coil and anti-magnetic shield followed by the circuit block, now reunited with the cleaned model number plate.

I secured the circuit block with a pair of screws borrowed from that spare 7546 movement because I did not want to refit the battery securing spring just yet. Pressing a fresh battery into the battery holder and I was relieved to see the movement spring into life. It looks as though it was just dirt and dried out lubrication that was preventing it from operating rather than any faults with any of the electrical components and so for the moment, that 7546 can breath easy.

Moving back to the calendar side, reassembly appeared to have gone smoothly but when testing the operation of the setting and quickset, I noticed that during the time setting operation, the rotation of the setting wheel was dragging the day/date correcting gear across to the intermediate day correction wheel, mounted on the minute wheel bridge, causing the latter to rotate. With the day wheel fitted this would result in the day wheel rotating inappropriately during the time-setting operation.

The reason it was doing this was that the setting wheel lever was not sitting low enough against the movement with the result that the underside framework was not staying hooked over the pin on the main plate (illustrated below in a photo of a spare 6309), thereby allowing the whole shebang to drag to the left.

I removed both the setting wheel lever and minute wheel bridge and gently bent both downwards slightly, with the result that the latter exerted a stronger force on the former when tightened down and the setting wheel lever then sat slightly lower. A retest and all seems well.

Attention now turns to the case. The usual breakdown into constituent parts

is followed by a thorough clean. Out with the old gaskets and crystal

and in with the new, together with a fresh battery.

The crystal, incidentally, is a tempered mineral facsimile of the original, complete with frosted chamfer and sourced from eBay seller kleinvintagewatchparts. You can see that lovely frosted chamfer in this shot of the crystal refitted to the case and awaiting the crystal retaining ring.

With the dial and hands refitted to the movement and the battery retaining spring back in position, it is time to fit the movement to the case,

close up the case back and turn over

before refitting the bezel.

The watch would originally have been fitted with a GL831 straight-vented rubber strap rather than the Z22 curved-vent strap it came on

and so with a modern equivalent secured (4FZ0AZ), we are all set to wrap this one up.

All that remains is to check the timekeeping and regulate as required. In this case, the watch was running a little fast for the first day or so but an eighth turn clockwise to the trimmer condenser and the watch has lost just under a second in the past 5 days, well within the specified accuracy of 15 seconds gain or loss per month. Let’s conclude with a wrist shot on the new strap.

Hi Martin, I enjoy reading through your posts and hope to get to watch disassembly at some point. In one of your earlier posts, and maybe here, you reference the 7548 as a mid grade diver in the Seiko lineup. Outside of the shrouded versions 7549, what else in the early eighties would have been a higher level diver offered by Seiko? I had read that the 7548 stayed in Japan during this period and the auto diver design and assembly team was moved to other countries, which kind of hints that these were the flagships of the lineup. What else did they offer in a higher finish or movement? Thanks, Dan

Hi Dan, my view on the hierarchy is defined by the relationship that was established between the 62MAS and 6105 150m divers of the early to late 1960’s and the higher end 300m 6215-7000 that appeared in 1967, followed by the high-beat 6159-7001 a year later. This higher end position was subsequently occupied by the 600m 6159-7010 and 7549 Tuna’s of the mid to late 1970’s (the latter in the context of the emergence of quartz technology as the state of the art) and later the 7C46 1000m Tuna of the mid 1980’s and beyond.

As soon as that first 6215 300m professional divers watch appeared in 1967, the 150m (and latterly 200m watches) could no longer be regarded as anything other than mid-tier watches, albeit watches that could be rightly regarded as professional divers watches. The fitment of quartz movements to the high end divers from the late 1970’s should not detract from the fact that these watches were constructed to a much higher level than the 150m 6309 and 7548 divers watches of the same period.

Thank you! The fitment of quartz does not detract at all as this was the leading technology at the time. I’ve taken a shine to the quartz diver’s of this era for their grab and go robustness. My first real watch was a gold faced Seiko 200m diver 5H26 quartz as a graduation gift. In my recent research of this model I’ve stumbled into this great resource, and have since purchased a 7548 and a 7549 to join the 5H26. It looks like I have the 3 tiers of build quality covered now and enjoying them all. I honestly went through the phase where I frowned on the quartz and had to have an auto, but practicality has put them idle in the drawer most of the time.

You are more fortunate than I. Thus far, I’ve yet to own a high end Seiko diver and those that I hanker after (6215 and 6159-7000’s) are now comfortably out of reach! Perhaps a modern MM300 is the answer 🙂

Hi Martin, I’m ordering some parts for this same model. I got the crystal from spencer Klien, I found the 3 gaskets. Does one need to change the crystal gasket normally? I have not been able to find that as easily. Second question, this watch has a click ball. My watch has the ball, but the bezel only clicks during half the rotation unless I push down harder. I have confirmed that this is the case with other bezels on same watch, and those bezels click fine on another 6309. My guess is the crystal ring is not seated properly. Does that sound correct with those symptoms? I guess my next purchase is a crystal press. Thanks.

I’m the proud owner of a 1982 7548-7000 which has been looked after by Neville Cox for Battery changes, replacement hands and bezel as needed. I have worn it continuously every day since I bought it. Not keeping it as a collectors piece, just my everyday wear. Does anybody have an ideas about where I can get a replacement face from?

It is always wonderful to hear from people who’ve owned and used such watches from new and for whom the patina is all self-inflicted!

As to a replacement dial, finding an original will be very difficult – close to impossible – unless sourced from a donor watch which has other issues. There are aftermarket options, but anything with Seiko branding that is produced by a third party will be of poor quality and to boot, in my book, constitutes fakery and so personally, I would rule out that option. You’ve not said why you wish to replace the dial. If it is just a matter of the lume, then you could consider getting it relumed but you will need to do some research to find someone who really knows what they are doing.

Andrew
I am about to advertise a 1982 7548-7000 for parts and the face is in excellent condition.It also has a Seiko metal band.
An ameteur watchmaker tried to get it going but it is either dirty (like Martin’s) or the coil is broken.
I give Martin permission to share my contact details with you as I would rather it go to a good home than an unknown person. bigaussie@shaw.ca

I don’t think these needed much more than a careful wipe with soft tissue wetted with lighter fluid and/or watchmaker’s putty. If you want to see a more extreme hands makeover, check out the most recent entries on the 6309-7040.

Hello Martin, I have the same watch, the serial number is 002964, imagine how old it is. I need a new green circuit block and a new calendar slide with the date in english and japanese, just like the one you show here. How can I get those parts? I live in Mexico City.
Thank You,
Adrian

Hi Adrian, probably the easiest solution to the circuit block problem is to find a used 7546 watch on eBay. The circuit block is identical to that of the 7548 but just marked differently. Ideally, you might even find a crown at 4 7546 with English/Kanji day disk and kill two birds with one stone. You could also try one of the specialist Seiko watch fora sales corners or post a WTB. Good luck!